This invention relates to photographic cameras having an electrically timed shutter, and more particularly to a shutter release control device which enables the shutter mechanism to operate in a mechanically timed mode as set from the electrically timed mode when the battery no longer supplies sufficient electrically energy.
In the use of electrical shutter control circuits, because power sources must generally be adapted for incorporation in the camera housing they therefore usually comprise batteries of small size and small capacity. When the electrical energy in the battery is dissipated with loss in voltage below a satisfactory operating level, the accuracy of shutter control is decreased to an unacceptable level as known in the art. Particularly with an electrically timed shutter of the type in which the opening operation of the shutter is mechanically actuated and the closing operation is controlled by the use of an electromagnet, when the voltage of the battery drops below the satisfactory operating level, the electromagnet is no longer effective to retain the rear shutter curtain or closing blade in an exposure aperture blocking position, with the result that the release actuation of the front shutter curtain or opening blade is immediately followed by accidental movement of the closing blade resulting in failure to expose the associated film. What is worse in this case is that the photographer is often not aware of the occurrence of such faulty operation.
In order to avoid this problem, a solution has been proposed as, for example, in U.S. Pat. No. 3,768,390. According to this proposal, when the normal operation of the electromagnet is not assured, the shutter release is locked, and thus the operator is unable to proceed to a later sequence of exposures. Such a conventional shutter release control device though advantageous from the standpoint of preventing the film from being fed without exposures tends to make difficult the ability to photograph under spontaneous circumstances even if one were willing to accept some loss in the accuracy of exposure control.